Small volume arc discharge lamps are now being developed for use as vehicle headlamps. These lamps offer long service lives, with high electrical efficiency. Moreover, these lamps have small optical sources, and can therefore provide overall improved headlamp optics. The enclosed volume of these lamps is roughly that of a pea, so the whole lamp may be conveniently formed initially from a small diameter quartz tube. Since the light source is small, the reflector optics may be made correspondingly small. The difficulty is then that the arc must be precisely located in the reflector. The lamp, when ignited, becomes quite hot, and therefore needs support by materials that can withstand the high operation temperature. Metals and ceramics have been used to support the arc tube, since these materials can easily withstand the high temperatures. Unfortunately, these materials are hard, and precise coupling of the arc tube with the metal or ceramic support structure can result in strain between the arc tube and the support. Since the practical manufacture of arc tubes, and metal or ceramic support structures normally results in some dimensional variation of the parts, some manufactured lamp tubes will have high contact, and stress, while others will have low contact and stress. The coupling stress is made worse by the thermal expansion and contraction of the components as the lamp is turned on and off. Arc tube fracture is then the final result in a portion of arc tubes pinched in metal support structures. There is then a need for an arc discharge headlamp capsule that can withstand the temperatures of operation, and still precisely locate the arc tube without excessive stress the arc tube.
A related problem concerns the energy management of the arc tube. The physics of the arc process is carefully designed for a particular operation temperature. Where thermal conduction from the arc tube differs, for example where the support structure has a low or high amount of contact with the arc tube, heat builds up, or is lost too quickly from the arc tube. The physics of the arc changes, thereby affecting the lamp optics, life and color. There is then a need for a support structure that from one arc tube to the next forms a consistent thermal contact.
Related prior patents include the following:
U.S. Pat. No. 4,734,612 issued to Hiroki Sasaki et al on Mar. 29, 1988 for a High Pressure Metal Vapor Discharge Lamp shows a double ended lamp capsule with leads welded to support wires. One support wire extends through a insulating sleeve and then, in parallel with the second wire, extend through a seal area of an enclosing capsule. Sasaki is generally concerned with an insulated preheater.
U.S. Pat. No. 4,754,373 issued to Lee W. Otto et al on Jun. 28, 1988 for a Automotive Headlamp shows a double ended filamented lamp capsule positioned in an automobile headlamp reflector. Otto shows generally how a double ended lamp capsule may be weleded and aligned axially as part of a headlamp.
U.S. Pat. No. 5,032,758 issued to John M. Davenport et al on Jul. 16, 1991 for a Precision Tubulation for Self Mounting Lamp shows an arc discharge axially aligned on a headlamp capsule.
U.S. Pat. No. 5,036,439 issued to Friedich Hoffmann et al on Jul. 30, 1991 for a Car Headlight Lamp and Method of Manufacturing Same shows a double ended arc discharge lamp capsule held in a metal reflector or shield. The reflector includes spring tabs that press against the lamp tube to properly position the shield.
U.S. Pat. No. 5,039,904 issued to Walter J. Kosmatka on Aug. 13, 1991 for a Mount for Miniature Arc Lamp shows a double ended arc discharge tube, axially mounted in a headlamp. One end of the tube is captured in a threaded structure including O-rings. The forward lead is ducted away from the capsule base to pass through the reflector body for exterior electrical connection.
U.S. Pat. No. 5,051,658 issued to Dirk Van Pijkeren on Sep. 24, 1991 for a an Electric High-Pressure Discharge Lamp for Use as a Motor Vehicle Headlamp shows a double ended arc discharge tube. The length of one end is pinched between two metal arms. The arms are supported on a bush that is in turn connected to a tube and holder body.
U.S Pat. No. 5,059,855 issued to Shinichi Irisawa et al on Oct. 22, 1991 for a Discharge Lamp Base Construction shows a double ended arc discharge tube welded by its leads at each end. The forward lead extends back through an insulating sleeve to a base. The leads are otherwise ducted through the body of the base.